Electrical insulation material



Feb. 8, 193s.

c. F. OBERMAIER 2,107,901

ELElITRICALIv INSULATION MATERIAL Original Filed Nov. 20, 1951.

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WWW/Wm A5 B ESTOS Mmmm CELLULOSE ACETATE ASB ESTO 5 Inventor: Carl P.Obermaier,

w www CLJ Hinctorneg Patented Feb. 8, 1938` UNITED STATES PATENT OFFICEELECTRICAL INSULATION MATERIAL Carl F. Obermaier, York, Pa., assignor toGeneral Electric Company, a corporation of New York 3 Claims.

The present application is a division of my copending applicationSerialNo. 576,433, led November 20, 1931, now Patent No. 2,038,378.

This invention relates to electrical insulation 5 material and tomethods of making the same.

Asbestos listing,.which is tape Woven from iine asbestos yarn, has beenused for some time in the electrical industry as insulation material.This tape has been diiiicult and expensive to'manufacture especially inthin sheets. -Such material as well as the so-called asbestos paper tapepossesses very little strength.

In accordance with the present invention asbestos either felted or inthe form of a ne paperlike material in sheet form is combined in asuitable manner with a cellulosic material, such as, for example,regenerated cellulose, known in the trade for instance as cellophane, ora cellulose derivative such as cellulose acetate. By the termlcellulosic material as hereinafter used, therefore, it is to beunderstood that such classes of material as enumerated above areincluded.

One practical result of my invention is the production of a sheet ortape of combined cellulosic material and felted asbestos which isadapted for use as insulation of wire in cable construction as morefully set forth in the copending application of Carl F. Obermaier andMurray H. Owen, Serial No. 558,535, led August 21, 1931, now Patent No.2,038,377 and assigned to the assignee of the present invention.

The cellulosic material not only lends strength to the asbestos but thecombined material is rendered high in dielectric value due to thecellulosic material and heat resistant due to the felted asbestos. Itmay be made in the form of sheets, tape, windings, etc. and may beimpregnated or coated with such materials as insulating varnishes,synthetic resins and the like, making the whole better in insulationvalue and eliminating subsequent coating operations Where the materialis used for example as a tape in insulating windings of electricalapparatus. In certain cases, the material may consist of a single sheetof cellulosic material combined on one or both sides thereof withasbestos or the asbestos may be sandwiched between a plurality of sheetsof cellulosic material and suitably combined therewith.

For a consideration of what is believed to be novel and the invention,attention is directed to the following specification, the accompanyingdrawing, and the claims appended thereto.

Figure 1, in the accompanying drawing illustrates one modification of myinvention, while Figures 2 and 3 illustrate further modifications of theinvention.

In accordance with one method of producing the insulation material of myinvention asbestos paper sheet known as asbestos felt, of suitablequality and thickness, depending on the conditions under which theinsulation material is to operate, is combined with cellulosic materialby simply using an adhesive to cause combination of the two. Forexample, where a cellulose derivative, for example, cellulose acetate iscombined with asbestos paper sheet, the sheet of cellulose acetate maybe treated with a varnish comprising an alkyd resin which may or may notcontain therein such modifying agents as natural resins, vegetable oilsand/or the acids derived,

therefrom as for example the drying oils like linseed, China-Wood oiland the like, or the acids derived from these oils. The asbestos paperis combinedv with the cellulose acetate, preferably under pressure, orpressure and heat, to cause firm adherence and the combined material iseither air dried or heat treated to cure the resin as the case mayrequire. Wherea non-resinous adhesive is used as for example, a watersoluble glue, the sheets may be combined directly under pressure andair-dried. In place of the cellulose acetate it is, of course,understood that other cellulosic materials such as enumerated heretoforemay be used.

In accordance with a further method of manufacturing the insulationmaterial of the invention the cellulosic material is employed inaplastic state-which it may be caused to assume by the use of heat and/orpressure and/or solvents and applied to asbestos sheet material using,if necessary, a suitable adhesive to aid in the combination of thematerials. After being thus brought together the combined material isoven treated to dry the same and expel solvents, if any are present inthe mass.

Where it is desired to prevent the asbestosI sheeting from absorbing toomuch adhesive a suitable sizing material, for example, starch, casein,etc. may be applied to the asbestos before the adhesive is applied.'I'his will insure less trouble in removing solvents and prevent theutilization of too much adhesive material.

A still further method to make the insulation material is to'prepare asuitable solution of the cellulosic material employed, and spray thelatter by means of suitable spray apparatus on felted asbestos as itpasses by the former on a. conveyor apron, drying the sprayed materialand repeating the spraying operations, it desired or necessary.

After the asbestos has gained some strength due to the initial spray thecombined material may be passed through a bath of the cellulosicmaterial and further coated in this way.

It is Within the scope of the present invention to utilize feltedasbestos in sheet form in connection with cellulosic material ofdiierent types in a single insulation. That is, the invention not onlycomprehends the combination of a single cellulosic material with feltedasbestos, but where desirable or necessary suitable combinations ofdifferent .types of cellulosic material may be used in making theinsulation material. For example, regenerated cellulose may be combinedwith felted asbestos which in turn may be combined with celluloseacetate and the whole if desired further coated or impregnated withinsulating varnishes, synthetic resins, etc.

Various obvious modifications will occur to those skilled in the art towhich the invention pertains, and it is desired to include all suchmodications within the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A unitary flexible electrical insulation material of high dielectricstrength composed of a continuous sheet of cellulose acetate united witha coextensive continuous sheet consisting of ielted asbestos. 2. Aunitary flexible insulation material of high dielectric strengthcomposed of a continuous sheet of cellulose acetate united on each sidethereof with felted asbestos in sheet form coextensive with said sheetof cellulose acetate.

3. An electrical insulation material comprising a sheet of ieltedasbestos faced on each side thereof with a sheet of cellulose acetate.

CARL F. OBERMAIER.

